Method for feeding a mixture comprising a burnable solid and water

ABSTRACT

The present invention is a method for feeding a mixture comprising a burnable solid and water to a combustion furnace or gasification reactor, comprising heating the mixture with a heater to convert at least a part of the water in the mixture into a form of steam and feeding the whole mixture to a combustion furnace or gasification reactor, wherein the whole mixture is transferred between an inlet of the heater and the combustion furnace or gasification reactor by a pump, characterized in that a discharge pressure at the pump is higher than an inner pressure in the combustion furnace or gasification reactor at least by 1.5 MPa and not higher than 22.12 MPa, and that a flow rate of said mixture with at least a part of the water being in a form of steam is from 6 to 50 m/s in a pipe in the heater and in a pipe between an outlet of the heater and an inlet of the combustion furnace or gasification reactor. The present invention provides a method for feeding a mixture of a burnable solid and water to a combustion furnace or gasification reactor, comprising heating the mixture with a heater to convert at least a part of the water in the mixture into a form of steam and feeding the whole mixture to a combustion furnace or gasification reactor, wherein almost no abrasion is caused in the pipes where the mixture flows and a stable feed of the mixture to a combustion furnace of a gasification reactor is attained without sedimentation of the burnable solid.

CROSS REFERENCES

This application claims the benefits of International Patent ApplicationWO2004/055436 filed on Dec. 11, 2003 and Japanese Patent Application2002-362202 filed on Dec. 13, 2002, the contents of which are therebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a method for feeding a mixturecomprising a burnable solid and water to a combustion furnace orgasification reactor, and more particularly, to a method for feeding theaforementioned mixture to a combustion furnace or gasification reactor,wherein at least a part of the water in the mixture is converted into aform of steam.

BACKGROUND OF THE INVENTION

As a means to feed a water slurry comprising a burnable solid, such aspulverized coal or a cellulosic solid waste, to a combustion furnace orgasification reactor, use was made of methods where a slurry is sprayeddirectly into a combustion furnace or gasification reactor with an aidof a high pressure gas, such as steam or air. The slurry contains waterin an amount of from 27 to 80 weight %, relative to the weight of theslurry, and the water vaporizes in a combustion furnace or gasificationreactor. In a slurry of pulverized coal and water, the water content isfrom 27 to 50%, relative to the weight of the slurry. A mixturecontaining a cellulosic solid waste and water sometimes fails to form aslurry, for instance, when the water content is at most 50% relative tothe weight of the mixture. Accordingly, some kinds of slurry require awater content of 50% or more, particularly of from 70 to 80%, relativeto the weight of the slurry, depending on the kind of cellulosic solidwaste. Therefore, a part of the energy generated in partial combustionof a burnable solid is consumed as latent heat for vaporization of thewater, which lowers a temperature in the furnace, resulting in anincrease in unburned carbon. In the gasification reactor, fused coal ashdeposits because of the lowered temperature in the gasification reactor.This causes troubles such as clog in a withdrawing line for fused ash.In order to prevent the troubles, the temperature in the furnace must beprevented from lowering. Accordingly a larger amount of oxygen than atheoretical amount calculated from an elemental composition of the coalis fed to a gasification reactor in the aforesaid conventional method.

In order to use pulverized coal containing ash of a high fusingtemperature, especially in gasification, the inner temperature of agasification reactor must be maintained at a relatively hightemperature. Accordingly, it is difficult in the conventional methods touse coal containing ash of a high fusing temperature. When such a coalcontaining ash of a high fusing temperature is unavoidably used, anexpensive melting point depressant should be used. In addition, a largeramount of oxygen is required to somewhat raise the inner temperature ofthe gasification reactor whereby melting of the coal ash in thegasification reactor is promoted so as to facilitate removal of the coalash at a bottom of the gasification reactor and thereby to put thegasification plant in smooth operations. A gasification efficiency ofthe conventional methods is low due to these factors.

A method of coal gasification by feeding coal and water to agasification reactor is known, where at least a part of water is fed ina form of steam to the gasification reactor (see Japanese PatentLaid-open No. 2002-155288). According to the method, coal is fed with anaid of steam to a gasification reactor. Therefore, water contained inthe mixture of coal and water, preferably the entire amount thereof, isvaporized into steam before being fed to the gasification reactor and,therefore, the above-described drawbacks can be solved.

In the above method, a mixture of solid-liquid system is converted intoa mixture of gas-solid or gas-liquid-solid system and fed to a reactor.As equipment by which a slurry of solid-liquid system is fed to a heatexchanger consecutively, heated, converted into a gas-solid system orgas-liquid-solid system, which is then fed to vaporization equipment torecover water, Cracksystem™ is commercially available from HosokawaMicron Co., Ltd. However, the solvent vaporizes at once in the heatexchanger in this equipment, so that a flow rate of the gas-solid systemat an outlet of the heat exchanger exceeds the sonic speed. Accordingly,if the equipment is used for a burnable solid such as coal, heavyabrasion will take place.

In 1979, patent application was filed by the Department of Energy,United States, in which a coal water mixture, CWM, is heated andseparated into gas and solid in a flash dryer vessel, and thenpulverized coal is fed to a gasification reactor (see U.S. Pat. No.4,153,427). However, the pulverized coal obtained in the gas-solidseparation is not completely dried and, therefore, coagulates, so that acontinuous feeding to the gasification reactor is difficult. Accordinglythe method has not been put to a practical application.

SUMMARY OF THE INVENTION

The present invention provides a method for feeding a mixture comprisinga burnable solid and water to a combustion furnace or gasificationreactor wherein at least a part of the water in the mixture is convertedinto a form of steam, and wherein almost no abrasion takes place inpiping and stable feeding to a combustion furnace or gasificationreactor is possible without sedimentation of the burnable solid.

In the conventional methods for feeding coal and water to a gasificationreactor to gasify the coal, there was a problem that heavy abrasiontakes place in pipes in the heater and a feeding pipe connected to thegasification reactor, if at least a part of the water is fed in a formof steam. In order to solve this problem, it might be thought to makeinner diameters of pipes in a heater and a feeding pipe large enough toreduce a flow rate of the fluid. However, if the inner diameters aremade large enough to suppress abrasion, other problems, in turn, arisesthat coal subsides on the inner wall of the pipes and further smoothconveying of the coal becomes difficult.

The inventors have made various researches to solve these problems. As aresult, the inventors have found that in pumping a mixture comprising aburnable solid and water to a combustion furnace or gasification reactorif a discharge pressure is controlled so as to be in the followingrelatively high specific range, the flow rate of the mixture may becontrolled properly with diameters of the pipes being set in a properrange to thereby feed the mixture to the above-mentioned reactors in astable manner without abrasion or sedimentation of the burnable solid inthe pipes through which the mixture flows.

Thus the present invention provides

-   (1) a method for feeding a mixture comprising a burnable solid and    water to a combustion furnace or gasification reactor, comprising    heating the mixture with a heater to convert at least a part of the    water in the mixture into a form of steam and feeding the whole    mixture to a combustion furnace or gasification reactor, wherein the    whole mixture is transferred between the heater and the combustion    furnace or gasification reactor by a pump, characterized in that a    discharge pressure at the pump is higher than an the inner pressure    in the combustion furnace or gasification reactor at least by 1.5    MPa and not higher than 22.12 MPa, and that a flow rate of said    mixture with at least a part of the water in the mixture being in a    form of steam is from 6 to 50 m/s in a pipe within the heater and in    a pipe between an outlet of the heater and an inlet of the    combustion furnace or gasification reactor.

Preferred embodiments are as follows:

-   (2) the method according to the above-described (1), wherein a    discharge pressure at the pump is higher than the inner pressure of    the combustion furnace or gasification reactor by from 3.0 MPa to    15.0 MPa;-   (3) the method according to the above-described (1), wherein a    discharge pressure at the pump is higher than an inner pressure in    the combustion furnace or gasification reactor by from 4.0 MPa to    15.0 MPa;-   (4) the method according to any one of the above-described (1)-(3),    wherein the above-described flow rate is from 8 to 40 m/s;-   (5) the method according to any one of the above-described (1)-(3),    wherein the above-described flow rate is from 10 to 40 m/s;-   (6) the method according to any one of the above-described (1)-(5),    wherein an inner diameter of the pipe in the heater becomes larger    gradually along a direction of the flow of the mixture, so that the    water is gradually converted into a form of steam;-   (7) the method according to any one of the above-described (1)-(5),    wherein an inner diameter of the pipe in the heater becomes larger    stepwise along a direction of the flow of the mixture, so that the    water is converted stepwise into a form of steam;-   (8) the method according to any one of the above-described (7),    wherein a pressure reducing valve is provided between sections of    the pipe with different diameters, so that the water in the mixture    is converted into a form of steam with an aid of the pressure    reducing valve;-   (9) the method according to any one of the above-described (7) or    (8), wherein an inner diameter of the pipe in the heater becomes    larger in from two to twelve steps;-   (10) the method according to any one of the above-described (7) or    (8), wherein an inner diameter of the pipe in the heater becomes    larger in from four to twelve steps;-   (11) the method according to any one of the above-described (7) or    (8), wherein an inner diameter of the pipe in the heater becomes    larger in from six to twelve steps;-   (12) the method according to any one of the above-described    (7)-(11), wherein a non-flammable gas is blown in just downstream of    a place where an inner diameter of the pipe becomes larger or a    place where a pressure reducing valve is provided;-   (13) the method according to anyone of the above-described (12),    wherein the non-flammable gas is steam, nitrogen, or gaseous carbon    dioxide;-   (14) the method according to any one of the above-described    (1)-(13), wherein substantially all of the water is converted into a    form of steam;-   (15) the method according to any one of the above-described    (1)-(14), wherein heating by the heater is carried out at a    temperature of from 150 to 450 degrees C. at a pressure of from 1.5    to 22.12 MPa;-   (16)the method according to any one of the above-described (1)-(14),    wherein heating by the heater is carried out at a temperature of    from 200 to 400 degrees C. at a pressure of from 3.0 to 22.12 MPa;-   (17) the method according to any one of the above-described    (1)-(14), wherein heating by the heater is carried out at a    temperature of from 200 to 365 degrees C. at a pressure of from 4.0    to 20.0 MPa;-   (18) the method according to any one of the above-described    (1)-(17), wherein heating is carried out with a heating medium at a    temperature of from 200 to 600 degrees C.;-   (19) the method according to any one of the above-described    (1)-(18), wherein a pressure control valve is provided between the    outlet of the heater and the combustion furnace or gasification    reactor;-   (20) the method according to any one of the above-described    (1)-(19), wherein a pre-heater is provided upstream of the heater;-   (21) the method according to the above-described (20), wherein a    pressure reducing valve is provided at the outlet of the pre-heater;-   (22) the method according to any one of the above-described    (1)-(21), wherein a water content in the mixture comprising a    burnable solid and water is from 27 to 80 weight %, relative to the    total weight of the mixture;-   (23) the method according to any one of the above-described    (1)-(21), wherein a water content in the mixture comprising a    burnable solid and water is from 30 to 40 weight %, relative to the    total weight of the mixture; and-   (24) the method according to any one of the above-described    (1)-(21), wherein a water content in the mixture comprising a    burnable solid and water is from 30 to 35 weight %, relative to the    total weight of the mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow chart of the device used in the Examples.

FIG. 2 is a graph to show a profile of the flow rate in the pipe betweenthe outlet of the pump and the inlet of the gasification reactor in theExample 1.

FIG. 3 is a graph to show a profile of the pressure in the pipe betweenthe outlet of the pump and the inlet of the gasification reactor inExample 1.

FIG. 4 is a graph to show a profile of the flow rate in the pipe betweenthe outlet of the pump and the inlet of the gasification reactor inExample 2.

FIG. 5 is a graph to show a profile of the flow rate in the pipe betweenthe outlet of the pump and the inlet of the gasification reactor inExample 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the water content of the mixture comprising a burnable solid andwater used in the present invention, the upper limit is preferably 80weight %, more preferably 40 weight %, and even more preferably 35weight %, and the lower limit is preferably 27 weight %, and morepreferably 30 weight %. Meanwhile, for the content of the burnablesolid, the upper limit is preferably 73 weight %, and more preferably 70weight%, and the lower limit is preferably 20 weight %, more preferably60 weight%, and ever more preferably 65 weight %. If the water contentexceeds the aforementioned upper limit and the content of the burnablesolid is less than the aforementioned lower limit, the energy tovaporize water is too large for the present method to be economical. Ifthe water content is less than the aforementioned lower limit and thecontent of the burnable solid exceeds the aforementioned upper limit,the mixture comprising the burnable solid and water is too viscous to betransferred smoothly. A surfactant may be added to facilitate formationof an aqueous slurry of a burnable solid.

The burnable solids subjected to combustion or gasification are notparticularly limited to specific kinds. Use may be made of, forinstance, coal, coal or petroleum coke, coal or petroleum pitch, orcellulosic solid waste. Coal of various coal ranks may be used, such asbituminous coal, sub-bituminous coal, or brown coal. Coal containing anash of a high melting point is difficult to use in a conventional methodwhere a coal/water slurry is fed to a gasification reactor. In thepresent invention, such a limitation caused by melting point of ash isimposed. The burnable solid is preferably pulverized to a desired grainsize before used. The grain size is preferably from 25 to 500 meshes,more preferably from 50 to 200 meshes. If the grain size of the coal istoo large, the coal particles cause very fast sedimentation in water.The coal is pulverized preferably in a dry state before mixed withwater, but it may be also pulverized in a wet state after mixed withwater.

The mixture comprising a burnable solid and water is fed by a pump to acombustion furnace or gasification furnace through a heater. As thepump, any known pump may be used, and mention may be made of, forinstance, a centrifugal pump, a plunger pump, or a gear pump.

The upper limit of the discharge pressure of the pump in the presentinvention is 22.12 MPa, which is the saturated steam pressure at thecritical temperature of water, 374.15 degrees C. The pressure ispreferably higher than a pressure in the combustion furnace orgasification furnace by 15.0 MPa, and more preferably by 10.0 MPa. Thelower limit is a pressure higher than a pressure in the combustionfurnace or gasification furnace by 1.5 MPa, preferably by 3.0 MPa, andmore preferably by 4.0 MPa. If the pressure exceeds the aforesaid upperlimit, large costs are needed to make apparatuses pressure-proof and,therefore, the method is uneconomical. If the pressure is lower than theaforementioned lower limit, more water will vaporize than desired and,therefore, the flow rate of the mixture becomes lower than the requiredflow rate as described below and, therefore, the burnable mixturesometimes cannot be smoothly transferred to the gasification reactor.

As the heater in the present invention, use may be made of any heaterthat can heat the above-described mixture and convert at least a part ofthe water in the mixture, preferably substantially all of the water,into a form of steam. For instance, a heating furnace or a heatexchanger may be used. Preferably, a heat exchanger, more preferably adouble tube heat exchanger, may be used.

In the present invention, it is needed that the flow rate of theaforementioned mixture in the pipe of the heater and in the pipe betweenthe outlet of the heater and the inlet of the combustion furnace orgasification reactor be in the following range; the upper limit of theflow rate: 50 m/s, preferably 40 m/s, and more preferably 30 m/s; andthe lower limit: 6 m/s, preferably 8 m/s, and more preferably 10 m/s.Thereby the mixture may be fed to the combustion furnace or gasificationreactor in a stable manner. If the flow rate exceeds-the aforementionedupper limit, the pipes wear out heavily. If the flow rate is lower thanthe aforementioned lower limit, the pipes easily clog because of thesedimentation of the burnable solid.

The inner diameter of the pipe in the heater through which the mixturecomprising a burnable solid and water passes preferably becomes largergradually, and more preferably stepwise along a direction of the flow ofthe mixture. Thereby the water in the mixture may be converted into aform of steam gradually or stepwise to control the flow rate of themixture properly. In an embodiment wherein an inner diameter of the pipebecomes larger stepwise, the inner diameter becomes larger in from 2 to12 steps, more preferably in from 4 to 12 steps, even more preferably infrom 6 to 12 steps. It is also preferred that pressure reducing valvesare provided between sections of the pipe with different innerdiameters, whereby a desired amount of the water in the mixture may beconverted into a form of steam properly. Preferably a non-flammable gasis blown just downstream of a place where an inner diameter of a pipebecomes larger or just downstream of a place where a pressure reducingvalve is provided. As the non-flammable gas, steam, nitrogen, or carbondioxide is preferably used. By blowing the non-flammable gas in, it ispossible to prevent the flow rate of the mixture in the pipe fromlowering, and to thereby maintain the flow rate of the mixture in thepipes in the desired range described above.

In the heater, the aforementioned mixture is heated to a temperature atwhich at least a part, preferably substantially all, of the water in themixture vaporizes and is converted into a form of steam. The upper limitof the heating temperature is preferably 450 degrees C., more preferably400 degrees C., and particularly preferably 365 degrees C. The lowerlimit is preferably 150 degrees C., more preferably 200 degrees C., andeven more preferably, 250 degrees C. If the temperature exceeds theaforementioned upper limit, a burnable solid, such as coal, causes anintense thermal decomposition and the resulting hydrocarbon substancesoften cause coking in the pipes, which leads to choke of the pipes inthe heater. Below the lower limit, water may not be sufficientlyvaporized. The pressure in the pipe in the heater during the heatingdescribed above depends on a discharge pressure of the pump and ispreferably from 1.5 to 22.12 MPa, more preferably from 3.0 to 22.12 MPa,and even more preferably from 4.0 to 20.0 MPa.

The aforementioned heating is carried out preferably by a heatingmedium, preferably heating oil or fused salt in a heat exchanger, suchas a double tube heat exchanger. A temperature of the heating medium ispreferably from 200 to 600 degrees C., more preferably from 250 to 500degrees C., and particularly preferably from 300 to 450 degrees C. Ifthe temperature exceeds the aforementioned upper limit, a burnablesolid, such as coal, causes thermal decomposition and the resultinghydrocarbon substances cause coking, which often leads to the choke ofthe pipe in the heater. Below the aforementioned lower limit, it isdifficult to heat the mixture to the desired temperature describedabove. A heater for heating the heating medium is not particularlyrestricted and any heater that can heat the heating medium to thedesired temperature described above may be used. Preferably a heatexchanger using a heating medium such as hot steam, hot oils, fusedsalts or gases may be used.

In the present invention, a pre-heater may be provided to heat themixture before the mixture is heated in the above-described heater,whereby the temperature at which the mixture is fed to a combustionfurnace or gasification reactor may be controlled properly, dependingupon an operation temperature of t he combustion furnace or gasificationreactor. The upper limit of the pre-heating temperature is preferably450 degrees C., more preferably 400 degrees C., and even more preferably365 degrees C. The lower limit is preferably 150 degrees C., morepreferably 200 degrees C., and even more preferably 250 degrees C. Thepressure in the pre-heating may be similar with the discharge pressureof the pump. The pre-heater aims to heat the mixture to a certaintemperature and, therefore, the pressure in a pipe in the pre-heater ispreferably equal to or higher than the saturated vapor pressure at theaforementioned desired temperature so as to prevent the water in themixture from evaporating. In order to keep this pressure, a pressurecontrol valve may preferably be provided at an outlet of the pre-heater.

The mixture comprising a burnable solid and water is heated to theaforementioned desired temperature in the heater, and at least a part,more preferably substantially all, preferably 95 weight % or more, andmore preferably 98 weight % or more, of the water is converted intosteam. The resulting steam pneumatically conveys the burnable solid andfeeds it to the combustion furnace or gasification reactor. Thecombustion furnace is preferably kept at a temperature of from 1,300 to2,000 degrees C., and more preferably from 1,300 to 1,700 degrees C.,under an atmospheric pressure or slightly pressurized condition to burnthe introduced burnable solid. Meanwhile, the gasification reactor iskept at a temperature of from 1,000 to 2,500 degrees C., more preferablyfrom 1,300 to 2,000 degrees C. at a pressure of from 0.5 to 10 MPa, morepreferably from 1 to 10 MPa, and even more preferably 2 to 10 MPa, togasify the introduced burnable solid. The combustion furnace orgasification reactor is preferably provided with a pressure controlvalve, capable of being fully closed, at the inlet, so that the amountof the mixture to be fed to the furnace may be properly controlled.

The method of the present invention may be applied to any knowncombustion or gasification methods to burn or gasify a mixturecontaining a burnable solid and water. As the gasification method,Texaco method and the Dow method may be mentioned.

The present invention will be explained in detail with reference to thefollowing Examples, but shall not be limited thereto.

EXAMPLES Example 1

The process flow shown in FIG. 1 was used in Example 1, wherein 1 is atank; 2, a pump; 3, a pipe; 4, a heater for a heating medium; 5, apre-heater; 6, a pressure control valve; 7, a first heater; 8, a secondheater; 9, a third heater; 10, a fourth heater; 11, a pipe; 12, apressure control valve; and 13, a gasification reactor. As the burnablesolid, pulverized coal A, general coal with a grain size of from 50 to200 meshes, was used. The pulverized coal was mixed with a given amountof water in a slurry maker, not shown, to prepare a mixture of coal andwater. The mixture was placed in tank 1 and stirring was continued toprevent sedimentation of the pulverized coal. The coal and watercontents and the viscosity of the mixture and the Higher Heating Value,the ash content of the coal, and the melting point of the ash from thecoal are as shown in the following Table 1.

TABLE 1 Mixture Coal Content 50.0 weight % Water Content 50.0 weight %Viscosity 4000 cp at 20 deg. C. to 170 cp at 95 deg. C. Coal Ash Content4.3 weight % Higher Heating Value (HHV) 3210 kcal/kg Melting Point ofAsh 1150 deg. C.

The above-described mixture of coal and water was pressurized with anaid of pump 2 to 11.76 MPa (120 kg/cm²), and then conveyed to pre-heater5 through line 3 in a flow amount of 130 kg/hour. The mixture pipe inpre-heater 5 was 6 mm in inner diameter and 80 m in total length. Here,the mixture was pre-heated to 300 degrees C. with a heating medium of340 degrees C. In a heater for heating medium 4. In order to prevent thewater in the mixture from evaporating in pre-heater 5 and also tocompensate pressure loss, the pressure in the pump side of the mixturepipe was maintained at a pressure of 10.58 MPa, (108 kg/cm²), which ishigher than the saturated vapor pressure of water at 300 degrees C.,approximately 8.82 MPa (approximately 90 kg/cm²). The flow rate of themixture in the pipe of pre-heater 5 was 1.16 m/s.

The mixture pre-heated to 300 degrees C. In pre-heater 5 was transferredto first heater 7 via pressure control valve 6. The mixture pipe offirst heater 7 was composed of a pipe of 2 mm in inner diameter×2 mlong, a pipe of 3 mm in inner diameter×4 m long, and a pipe of 4 mm ininner diameter×4 m long, the total length, 10 m along a direction of theflow of the mixture. The mixture was heated also in this pipe with aheating medium of 340 degrees C. In first heater 7, a part of the waterof the mixture evaporated. The flow rate of the mixture in the pipe offirst heater 7 was 11.5 m/s at a pressure of 9.18 MPa (93.7 kg/cm²) atthe inlet, with the inner diameter being 2 mm, and 27.95 m/s at theoutlet, with the inner diameter being 4 mm. The temperature at theoutlet was 268 degrees C. and the pressure at the outlet was 5.24 MPa(53.5 kg/cm²).

The mixture which left first heater 7 was conveyed to second heater 8. Amixture pipe in second heater 8 was 6 mm in inner diameter and 10 m intotal length. Here the mixture was again heated with a heating medium of340 degrees C. Further, a part of the water in the mixture vaporized dueto the adiabatic expansion in second heater 8. The flow rate of themixture in the pipe of second heater 8 was 12.55 m/s at the inlet and29.25 m/s at the outlet. At the outlet the temperature was 255 degreesC. and the pressure was 4.19 MPa (42.8 kg/cm²).

The mixture which left second heater 8 was then conveyed to third heater9. A mixture pipe in third heater 9 was 8 mm in inner diameter and 10 min total length. Here the mixture was again heated with a heating mediumof 340 degrees C. Further, a part of the water in the mixture vaporizeddue to the adiabatic expansion in third heater 9. The flow rate of themixture in the pipe of third heater 9 was 16.45 m/s at the inlet and33.02 m/s at the outlet. At the outlet the temperature was 245 degreesC. and the pressure was 2.8 MPa (28.6 kg/cm²).

The mixture which left third heater 9 was conveyed to fourth heater 10.The mixture pipe in fourth heater 10 was 12 mm in inner diameter and 30m in total length. Here the mixture was again heated with a heatingmedium of 340 degrees C. Further, a part of the water in the mixturevaporized due to the adiabatic expansion in fourth heater 10 and, afterall, substantially all of the water in the mixture introduced into theheaters was converted into steam. The flow rate of the mixture in thepipe of fourth heater 10 was 11.3 m/s at the inlet and 35.76 m/s at theoutlet. At the outlet the temperature was 300 degrees C. and thepressure was 1.96 MPa (20 kg/cm²).

The mixture thus heated was introduced via line 11 and control valve 12to gasification reactor 13 where the pressure was maintained at 1.96 MPa(20 kg/cm²). In the gasification reactor, the pulverized coal wasgasified according to a known method. The flow rate in line 11 wasalmost equal to that at the outlet of fourth heater 10.

FIGS. 2 and 3 show changes in flow rates and pressures between theoutlet of pump 2 and gasification reactor 13. The flow rate of themixture was calculated from the pressures and temperatures in the pipesof each heater.

The above steps were continued for 50 hours, during which stableoperations could be attained without sedimentation of the pulverizedcoal. After the operations, the pipe connecting to the gasificationreactor and the inlet and the outlet of the control valve 12, where theflow rate through the piping became fastest, were inspected visually tofind almost no abrasion on each inner wall.

Example 2

In Example 2, the same process flow as in Example 1, shown in FIG. 1,was used. The viscosity of the mixture used in Example 2 was differentfrom that of the mixture used in Example 1 since the type of thepulverized coal was different as shown below. Accordingly, lengths ofthe mixture pipes in the pre-heater and the heaters were changed so thatstable operations would be secured over a long time. As the burnablesolid, pulverized coal B, general coal with a grain size of from 50 to200 meshes, was used instead of the pulverized coal A to prepare amixture of coal and water according to the same procedures as Example 1.The coal and water contents and the viscosity of the mixture and thehigher heating value, the ash content, and the melting point of the ashof the coal are as shown in the following. Table. 2.

TABLE 2 Mixture Coal Content 50.0 weight % Water Content 50.0 weight %Viscosity 400 cp at 20 deg. C. to 70 cp at 95 deg. C. Coal Ash Content9.5 weight % Higher Heating Value (HHV) 7090 kcal/kg Melting Point ofthe Ash 1450 deg. C.

A mixture of the aforesaid coal and water was pressurized to 9.87 MPa(100.6 kg/cm²) with pump 2 and then was conveyed to pre-heater 5 vialine 3 in a flow amount of 140 kg/hour. A mixture pipe in pre-heater 5was 6 mm in inner diameter and 73 m in total length. In this pipe, themixture was pre-heated to 300 degrees C. with a heating medium heated to310 degrees C. in a heater for heating medium 4. In order to preventwater in the mixture from vaporizing in pre-heater 5 and to compensatepressure loss, the pressure in the pump side of the mixture pipe wasmaintained at 9.25 MPa (94.3 kg/cm²), which pressure was higher than thesaturated vapor pressure of water at 300 degrees C., approximately 8.82MPa (approximately 90 kg/cm²). The flow rate of the mixture in the pipeof pre-heater 5 was 1.3 m/s.

The mixture pre-heated to 300 degrees C. in pre-heater 5 was conveyed tofirst heater 7 via pressure control valve 6. The mixture pipe of firstheater 7 was composed of a pipe of 2 mm in inner diameter×3 m long, apipe of 3 mm in inner diameter×2 m long, and a pipe of 4 mm in innerdiameter×2 m long joined in this order toward the gasification reactoralong with the direction of the flow, and the total length was 7 m. Themixture was again heated in this pipe with a heating medium of 310degrees C. In first heater 7, a part of the water of the mixturevaporized. The flow rate of the mixture in first heater 7 was 13.4 m/sat a pressure of 8.97 MPa (91.5 kg/cm²) at the inlet of the pipe, withthe inner diameter of 2 mm, and 23.7 m/s at the outlet of the pipe, withthe inner diameter of 4 mm. The temperature at the outlet was 252degrees C. and the pressure at the outlet was 4.03 MPa (41.1 kg/cm²).

The mixture which left first heater 7 was conveyed to second heater 8.The mixture pipe of second heater 8 was 6 mm in inner diameter and 11.5m in total length. The mixture was heated also here with a heatingmedium of 310 degrees C. A part of the water in the mixture vaporizedfurther due to the adiabatic expansion in second heater 8. The flow rateof the mixture in second heater 8 was 10.8 m/s at the inlet of the pipeand 19.9 m/s at the outlet. At the outlet the temperature was 245degrees C. and the pressure was 3.55 MPa (36.2 kg/cm²).

The mixture which left second heater 8 was conveyed to third heater 9.The mixture pipe of third heater 9 was 8 mm in inner diameter and 16.5 min total length. The mixture was heated also here with a heating mediumof 310 degrees C. A part of the water in the mixture vaporized furtherdue to the adiabatic expansion in third heater 9. The flow rate of themixture in third heater 9 was 11.4 m/s at the inlet and 25.8 m/s at theoutlet. At the outlet the temperature was 227 degrees C. and thepressure was 2.54 MPa (25.9 kg/cm²).

The mixture which left second heater 9 was conveyed to fourth heater 10.The mixture pipe of fourth heater 10 was 12 mm in inner diameter and 19m in total length. The mixture was heated also here with a heatingmedium of 310 degrees C. A part of the water in the mixture vaporizedfurther due to the adiabatic expansion in fourth heater 10 and, afterall, substantially all of the water in the mixture introduced into theheaters was converted into steam. The flow rate of the mixture in fourthheater 10 was 11.7 m/s at the inlet and 19.9 m/s at the outlet. At theoutlet the temperature was 244 degrees C. and the pressure was 1.96 MPa(20 kg/cm²).

The mixture thus heated was introduced via line 11 and control valve 12to gasification reactor 13 maintained at a pressure of 1.96 MPa (20kg/cm²). In the gasification reactor, the pulverized coal was gasifiedaccording to a known method. The flow rate of the mixture in line 11 wasalmost equal to that at the outlet of fourth heater 10.

Profiles of the flow rates and pressures of the mixture from the outletof pump 2 to gasification reactor 13 described above are shown in FIGS.4 and 5. The flow rate of the mixture was calculated from the pressuresand temperatures in the pipes of each heater.

The aforementioned steps were continued for 50 hours, during whichstable operations were attained without sedimentation of the pulverizedcoal. After the operations, the pipe connecting to the gasificationreactor and the inlet and the outlet of the control valve 12, where theflow rate through the pipes became fastest, were inspected visually tofind almost no abrasion on each inner wall as in Example 1.

INDUSTRIAL APPLICABILITY

The present invention provides a method for feeding a mixture comprisinga burnable solid and water to a combustion furnace or gasificationreactor wherein at least a part of the water in the mixture is convertedinto a form of steam, and wherein almost no abrasion takes place inpiping and stable feeding to a combustion furnace or gasificationreactor is possible without sedimentation of the burnable solid.

1. A method for feeding a mixture comprising a burnable solid and waterto a combustion furnace or gasification reactor, comprising: heating themixture with a heater to convert at least a part of the water in themixture into a form of steam; and feeding the whole mixture to acombustion furnace or gasification reactor, wherein the whole mixture istransferred between an inlet of the heater and the combustion furnace orgasification reactor by a pump, a discharge pressure at the pump ishigher than an inner pressure in the combustion furnace or gasificationreactor at least by 1.5 MPa and not higher than 22.12 MPa, a flow rateof said mixture with at least a part of the water being in a form ofsteam is from 6 to 50 m/s in a pipe in the heater and in a pipe betweenan outlet of the heater and an inlet of the combustion furnace orgasification reactor, and an inner diameter of the pipe in the heaterbecomes larger gradually or stepwise along a direction of the flow ofthe mixture, so that the water in the mixture is gradually or stepwiseconverted into a form of steam.
 2. The method according to claim 1,wherein a discharge pressure at the pump is higher than an innerpressure of the combustion furnace or gasification reactor by from 3.0MPa to 15.0 MPa.
 3. The method according to claim 1, wherein a dischargepressure at the pump is higher than an inner pressure in the combustionfurnace or gasification reactor by from 4.0 MPa to 15.0 MPa.
 4. Themethod according to claim 1, wherein said flow rate is from 8 to 40 m/s.5. The method according to claim 1, wherein said flow rate is from 10 to40 m/s.
 6. The method according to claim 1, wherein an inner diameter ofthe pipe in the heater becomes larger gradually along a direction of theflow of the mixture, so that the water in the mixture is graduallyconverted into a form of steam.
 7. The method according to claim 1,wherein an inner diameter of the pipe in the heater becomes largerstepwise along a direction of the flow of the mixture, so that the waterin the mixture is stepwise converted into a form of steam.
 8. The methodaccording to claim 7, wherein a pressure reducing valve is providedbetween sections of the pipe with different diameters, so that the waterin the mixture is converted into a form of steam with an aid of thepressure reducing valve.
 9. The method according to claim 7, wherein aninner diameter of the pipe in the heater becomes larger in from 2 to 12steps.
 10. The method according to claim 7, wherein an inner diameter ofthe pipe in the heater becomes larger in from 4 to 12 steps.
 11. Themethod according to claim 7, wherein an inner diameter of the pipe inthe heater becomes larger in from 6 to 12 steps.
 12. The methodaccording to claim 7, said non-flammable gas is blown in just downstreamof a place where the inner diameter of the pipe becomes larger.
 13. Themethod according to claim 12, wherein said non-flammable gas is steam,nitrogen, or carbon dioxide.
 14. The method according to claim 1,wherein substantially all of the water is converted into a form ofsteam.
 15. The method according to claim 1, wherein the heating by theheater is carried out at a temperature of from 150 to 450 degrees C at apressure of from 1.5 to 22.12 MPa.
 16. The method according to claim 1,wherein the heating by the heater is carried out at a temperature offrom 200 to 400 degrees C at a pressure of from 3.0 to 22.12 MPa. 17.The method according to claim 1, wherein the heating by the heater iscarried out at a temperature of from 200 to 365 degrees C at a pressureof from 4.0 to 20.0 MPa.
 18. The method according to claim 1, whereinthe heating is carried out with a heating medium of a temperature offrom 200 to 600 degrees C.
 19. The method according to claim 1, whereina pressure control valve is provided between the outlet of the heaterand the inlet of the combustion furnace or gasification reactor.
 20. Themethod according to claim 1, wherein a pre-heater is provided upstreamof the heater.
 21. The method according to claim 20, wherein a pressurereducing valve is provided at the outlet of the pre-heater.
 22. Themethod according to claim 1, wherein a water content in the mixturecomprising a burnable solid and water is from 27 to 80 weight %,relative to the total weight of the mixture.
 23. The method according toclaim 1, wherein a water content in the mixture comprising a burnablesolid and water is from 30 to 40 weight %, relative to the total weightof the mixture.
 24. The method according to claim 1, wherein a watercontent in the mixture comprising a burnable solid and water is from 30to 35 weight %, relative to the total weight of the mixture.